Sodium chloride and magnesium chloride solutions have been used for deicing of road and roadway structures for many years. Sodium chloride is readily available and is inexpensive. however, the use of sodium chloride has several disadvantages; it has an adverse effect on roadside vegetation and the groundwater, and it severely corrodes roadside barriers, bridges and the like, as well as the vehicles that drive over them, adding to the overall costs of using sodium chloride. Thus a search has been ongoing for some time to replace sodium chloride as a deicer with a less corrosive material.
Other salts have been suggested, but either they are too expensive, unavailable in quantity, or they are also corrosive.
Calcium chloride is less corrosive than sodium chloride, but is still corrosive to metals. The use of calcium chloride as a deicer composition is advantageous because it generates heat when it hits solidified water such as snow or ice, further promoting deicing. Various corrosion inhibitors have been tried. The use of chromates as corrosion inhibitors for calcium chloride brine solutions is known; however, the use of chromates is being discouraged because they harm the environment. The use of nitrites has also been suggested, but a high level of the nitrite in calcium chloride is required as a corrosion inhibitor.
Zefferi et al in U.S. Pat. No. 5,292,455 have disclosed the addition of 2-hydroxyphosphorus acetic acid to calcium chloride brines as a corrosion inhibitor, effective in amounts of 240-1000 ppm of the additive in the brine solution, but this additive is expensive.
U.S. Pat. No. 5,296,167 to Murray suggests the substitution of calcium chloride solutions for sodium chloride as a deicer. Since calcium chloride is also corrosive, this reference discloses the addition of orthophosphates as corrosion inhibitors. However, large amounts of the inhibitors are required, up to 40 grams/gallon of brine. This solution must also contain pH buffers such as calcium carbonate and magnesium hydroxide, all of which add to the cost of these solutions. Further, these additives can find their way into sewers and public waterways.
Thus an inexpensive, effective deicer composition that is less corrosive than sodium chloride would be of interest.